Ok, here's my version, as promised:
Instalation:
- unzip archive
- connect your reader to the computer
- copy everything from "card" directory to your card (your original autorun.* files will be overwritten - back them up, if you think you'll need them)
- copy everything from "prs" directory to internal memory of your Sony Reader
- disconnect reader - the program should start
What's new:
- search via grep - features are the same as described by =X=
- additional button for clearing all text from input field (marked '<<')
- prev/next line buttons working (expect slight delay after first keypress, after that it's pretty much immediate)
- status line showing some additional info for user added - not used heavily in the current version, but might be useful in the future
Following might be of interest to programers

:
- I have everything prepared for showing of "hourglass" icon during the search, but unfortunately I haven't found the way how to force-update the screen while a function is running (normaly, redraw is done only when reader is "idle") - as a result, the icon would show only after the search is completed

- The program itself should be now more modular & readable for other contributors - I rewrote major parts of the code, renamed variables/functions to English and added a lots of comments. You tell me if it's for better or not.

- A slightly different way of input-mapping can be activated by setting "threeButton" to true - description of the mapping is in the code.
Well, that's it. Let me know if you find it useful (or if it's at least running...). Once againg, big thanks to Clemenseken for making such a great & useful program!